Optimal climbing speed explains the evolution of extreme sexual size dimorphism in spiders

Several hypotheses have been put forward to explain the evolution of extreme sexual size dimorphism (SSD). Among them, the gravity hypothesis (GH) explains that extreme SSD has evolved in spiders because smaller males have a mating or survival advantage by climbing faster. However, few studies have supported this hypothesis thus far. Using a wide span of spider body sizes, we show that there is an optimal body size (7.4 mm) for climbing and that extreme SSD evolves only in spiders that: (1) live in high‐habitat patches and (2) in which females are larger than the optimal size. We report that the evidence for the GH across studies depends on whether the body size of individuals expands beyond the optimal climbing size. We also present an ad hoc biomechanical model that shows how the higher stride frequency of small animals predicts an optimal body size for climbing.     

Diet affects female mating behaviour in a seed‐feeding beetle

In species where males provide nuptial gifts, females can improve their nutritional status and thus increase their fecundity by mating when in need of resources. However, mating can be costly, so females should only mate to acquire resources when the need for resources is large, such as when females are nutritionally‐deprived. Two populations of the seed‐feeding beetle Callosobruchus maculatus, a species that produces relatively large nuptial gifts, are used to test whether female nutritional status affects mating behaviour. Female access to water, sugar and yeast are manipulated and the fitness consequences of these manipulations are examined together with the effects of diet on the propensity of nonvirgin females to mate. Access to water has a small but significant effect on mass loss over time, lifespan and fecundity of females, relative to unfed controls. Access to sugar (dissolved in water) improves female fecundity and lifespan above that of hydrated females but access to yeast has no positive effects on female survival or reproduction. Diet has a large effect on both receptivity of nonvirgin females to a male and how quickly they accept that male. Unfed females are both more likely to mate, and accept a mate more quickly, than females provided access to water, which are more likely to mate and accept a mate more quickly than females provided with sugar. This rank order of behaviours matches the order predicted if females increase their mating rate when nutritionally deprived (i.e. it matches the effect of diet on female fitness). The results obtained also suggest that mate choice may be condition‐dependent: females from one population (Burkina Faso) show a preference for large males when well‐fed but not when unfed, although this result is not found in a second population (South India). It is concluded that nutritionally‐deprived females are more receptive to mates than are well‐fed females, consistent with the hypothesis that females ‘forage’ for nuptial gifts, or at least more willingly accept sperm in exchange for nuptial gifts, when they are nutritionally deprived.     

Resurrecting the differential mortality model of sexual size dimorphism

In some animal groups males may be several times smaller than females. One of the hypotheses proposed to explain the evolution of this extreme sexual size dimorphism (SSD) is the differential mortality model (DMM), which is based on the assumption that when males are the searching sex, higher male mortality relaxes male–male contest competition, leading to the adaptive evolution of early‐maturing, small males that are favoured by viability selection. Evidence for the main prediction of this model, i.e. that there is a negative relationship between differential mortality and SSD, has remained elusive. Using sex differences in pitfall trap catches – a proxy of sex differences in mobility and mortality – across 40 spider species, and using the evolutionary comparative method, we found significant negative relationships between differential mortality and SSD for three size traits. Thus, the DMM can still explain part of the observed variance in SSD.     

DESCRIPTION OF THE SENSORY CHARACTERISTICS OF SPANISH UNIFLORAL HONEYS BY FREE CHOICE PROFILING

Different Spanish unifloral honeys (eucalyptus, sunflower, rosemary, thyme, lavender, citrus, anise, quercus, and lemon blossom) and one multifloral honey were studied by Free-Choice Profiling (FCP) analysis. Generalized Procrustes Analysis (GPA) applied to the FCP data allowed discrimination between samples and provided information on the attributes responsible for the differences observed. The honeys had significantly different sensory characteristics. Textural attributes were the predominant factor in discriminating between samples, and appearance (color included) was also correlated with GPA dimensions to a lesser extent.     

Long-term growth at elevated carbon dioxide stimulates methane emission in tropical paddy rice

Recent anthropogenic emissions of key atmospheric trace gases (e.g. CO₂ and CH₄) which absorb infra-red radiation may lead to an increase in mean surface temperatures and potential changes in climate. Although sources of each gas have been evaluated independently, little attention has focused on potential interactions between gases which could influence emission rates. In the current experiment, the effect of enhanced CO₂ (300 μL L^–1 above ambient) and/or air temperature (4 °C above ambient) on methane generation and emission were determined for the irrigated tropical paddy rice system over 3 consecutive field seasons (1995 wet and dry seasons 1996 dry season). For all three seasons, elevated CO₂ concentration resulted in a significant increase in dissolved soil methane relative to the ambient control. Consistent with the observed increases in soil methane, measurements of methane flux per unit surface area during the 1995 wet and 1996 dry seasons also showed a significant increase at elevated carbon dioxide concentration relative to the ambient CO₂ condition (+49 and 60% for each season, respectively). Growth of rice at both increasing CO₂ concentration and air temperature did not result in additional stimulation of either dissolved or emitted methane compared to growth at elevated CO₂ alone. The observed increase in methane emissions were associated with a large, consistent, CO₂-induced stimulation of root growth. Results from this experiment suggest that as atmospheric CO₂ concentration increases, methane emissions from tropical paddy rice could increase above current projections.     

A genetic background with low mutational robustness is associated with increased adaptability to a novel host in an RNA virus

Although mutational robustness is central to many evolutionary processes, its relationship to evolvability remains poorly understood and has been very rarely tested experimentally. Here, we measure the evolvability of Vesicular stomatitis virus in two genetic backgrounds with different levels of mutational robustness. We passaged the viruses into a novel cell type to model a host‐jump episode, quantified changes in infectivity and fitness in the new host, evaluated the cost of adaptation in the original host and analyzed the genetic basis of this adaptation. Lineages evolved from the less robust genetic background demonstrated increased adaptability, paid similar costs of adaptation to the new host and fixed approximately the same number of mutations as their more robust counterparts. Theory predicts that robustness can promote evolvability only in systems where large sets of genotypes are connected by effectively neutral mutations. We argue that this condition might not be fulfilled generally in RNA viruses.     

An enigmatic actinopterygian (Pisces: Osteichthyes) from the Upper Permian of China

A new actinopterygian fish Yaomoshania minutosquama gen. & sp. nov., from the Upper Permian of the Dzungaria [Junggar] Basin in China is described. The material consists of two very fragmentary specimens showing almost exclusively scale rows. The arrangement of the scale rows of the holotype resembles the reversion lines of acanthodian caudal fins and of cheirolepids. The size and shape of the scales, and the diminishing size of the scales along the rows, is similar to those of acanthodians and those actinopterygians with small scales such as Cheirolepis. However, the histology of the scales demonstrates features that are found in more advanced actinopterygians: superimposed ganoine lamellae, the arrangement of dentine tubules and pulp canals, buried odontodes stacked on each other to make the ornamental ridges, and an asymmetric pattern of growth achieved by extensive remodelling (resorption and redeposition) of all layers of the scale. Yaomoshania minutosquama is proposed as a small-scale bearing, basal actinopterygian, different from Cheirolepis , but characterized by advanced histological characters.